BK channel inactivation gates daytime excitability in the circadian clock

Joshua P. Whitt, Jenna R. Montgomery& Andrea L. Meredith

Nature Communications 7, Article number: 10837 doi:10.1038/ncomms10837
Received 04 August 2015 Accepted 26 January 2016 Published 04 March 2016

Inactivation is an intrinsic property of several voltage-dependent ion channels, closing the conduction pathway during membrane depolarization and dynamically regulating neuronal activity. BK K+ channels undergo N-type inactivation via their β2 subunit, but the physiological significance is not clear. Here, we report that inactivating BK currents predominate during the day in the suprachiasmatic nucleus, the brain’s intrinsic clock circuit, reducing steady-state current levels. At night inactivation is diminished, resulting in larger BK currents. Loss of β2 eliminates inactivation, abolishing the diurnal variation in both BK current magnitude and SCN firing, and disrupting behavioural rhythmicity. Selective restoration of inactivation via the β2 N-terminal ‘ball-and-chain’ domain rescues BK current levels and firing rate, unexpectedly contributing to the subthreshold membrane properties that shift SCN neurons into the daytime ‘upstate’. Our study reveals the clock employs inactivation gating as a biophysical switch to set the diurnal variation in suprachiasmatic nucleus excitability that underlies circadian rhythm.

失活是幾種電壓依賴性離子通道的內(nèi)在特性，在膜去極化過程中關(guān)閉傳導(dǎo)通路，及動(dòng)態(tài)調(diào)節(jié)神經(jīng)元活動(dòng)。BK K（+）通道通過β2亞基進(jìn)行N型失活，但該失活在生理意義上尚不明確。在最近一篇于Nature Communication所發(fā)表的報(bào)告中，巴爾的摩馬里蘭大學(xué)的研究人員發(fā)現(xiàn)大腦的內(nèi)部時(shí)鐘電路 - 視交叉上核 -于白天時(shí)中失活的BK電流占主導(dǎo)地位，減少穩(wěn)態(tài)電流水平。晚上失活減少，導(dǎo)致更大的BK電流。失去β2亞基消除失活，并消除了BK電流水平及SCN發(fā)射率的晝夜變化，也破壞了行為節(jié)律。通過β2亞基N-端的 “球和鏈” 域進(jìn)行選擇性恢復(fù)失活，可拯救BK電流水平和發(fā)射率，卻意外地導(dǎo)致了膜的亞閾性質(zhì)，該性質(zhì)把SCN神經(jīng)元轉(zhuǎn)變?yōu)榘滋鞛椤鄙稀钡臓顟B(tài)。研究人員揭示了該生物時(shí)鐘采用失活門作為一種生物物理開關(guān)設(shè)置，從而控制視交叉上核興奮性的晝夜變化并導(dǎo)致晝夜節(jié)律。

本項(xiàng)研究關(guān)鍵儀器之一為MED64系統(tǒng)，通過MED64系統(tǒng)處理實(shí)驗(yàn)?zāi)X切片并對(duì)SCN神經(jīng)元電生理信號(hào)進(jìn)行多電極陣列記錄。MED64系統(tǒng)是由日本ALPHA MED SCIENTIFIC研發(fā)生產(chǎn)的電生理信號(hào)記錄系統(tǒng)，旨在幫助更多的科研者提升電生理領(lǐng)域的研究。MED64系統(tǒng)被廣泛應(yīng)用于中央和周圍神經(jīng)系統(tǒng)以及心臟等課題的研究，無論對(duì)于急性切片還是培養(yǎng)的細(xì)胞組織來說，MED64系統(tǒng)都能提供良好的研究方法。尤其在急性切片信號(hào)記錄方面，MED64系統(tǒng)具有無與倫比的低噪聲電極配合內(nèi)置的刺激器使得突觸電位更易誘發(fā)，用戶友好的軟件界面使用戶對(duì)數(shù)據(jù)處理完全無后顧之憂。另外該公司最新開發(fā)的MED64-Neurolyte系統(tǒng)為專門給神經(jīng)細(xì)胞研究之用，歡迎各研究神經(jīng)細(xì)胞胞外電場(chǎng)的科研人員試用。

原文鏈接：http://www.nature.com/ncomms/2016/160304/ncomms10837/full/ncomms10837.html